Well when you go out walking, be sure to go out in a STRAIGHT PATH. Try not to venture left or right. Just go down a road and take it to the end, as the gps system has shown to take your starting point, your end point (after x amount of minutes), and compute the shortest distance possible, disregarding walking along streets.
I haven't really experienced this issue of not hatching, or I haven't noticed it. Perhaps its also just your connection that suffers, or perhaps its really a bug. Either way, I've never had an egg stall for more than a day like this.
I know this system is weird and unusual, but it's been reported that way. It's like the different between Distance and Displacement, in physics terms. You run a lap around a track. Distance says you ran 400m, but Displacement says you ran 0m because you're in the same spot.
http://comicbook.com/2016/07/21/pokemon-go-eggs-may-not-work-the-way-you-think/ This is just the first site I saw that mentions the tracking system, and the information is conclusive with reports.
If you need more information, just search "Pokemon Go eggs tracking system" in google. Click any page that relates to misconceptions/untold secrets/incorrect. These are the pages that acknowledge how the system is different from a normal GPS